Chromocene, ferrocene, cobaltocene, and nickelocene derivatives with isopropyl and methyl or trimethylsilyl substituents

• Dimethyl-diisopropylcyclopentadienyl ligands confer solubility and crystallinity.
• No other high spin chromocenes found among alkylated or silylated derivatives.
• Efficient transfer of a C5H5 ligand from nickelocene to a cationic nickel fragment.

From sodium 2,3-diisopropyl-1,4-dimethyl-cyclopentadienide and MBr2(dme) (M = Fe, Co, Ni) the corresponding ferrocene (1), cobaltocene (2) and nickelocene (3) could be obtained as pure, crystalline solids. From an analogous reaction of sodium 2,3,5-triisopropyl-1,4-dimethyl-cyclopentadienide with FeCl2, only the mixed-substituted ferrocene (C23p)(C22p)Fe (4) could be crystallized (C23p = 2,3,5-triisopropyl-1,4-dimethyl-cyclopentadienyl, C22p = 2,3-diisopropyl-1,4-dimethyl-cyclopentadienyl). The trimethylsilyl substituted ferrocene (5) and nickelocene (6) were synthesized from the corresponding metal halides and potassium 2,3-diisopropyl-1,4-dimethyl-5-trimethylsilyl-cyclopentadienide as well as a series of chromocenes with silylated or alkylated cyclopentadienyl ligands (7–10) from chromium(II) acetate. Octaisopropylnickelocene (11) has been obtained and converted to octaisopropylnickelocenium hexafluorophosphate (12). 1,2,3,4-tetraisopropylnickelocenium tetrabromoaluminate (13) was obtained from tetraisopropylcyclopentadienylnickel(II) tetrabromoaluminate and nickelocene. Crystal structures have been obtained for metallocenes 1–5, 7–9, and 11.

Metallocenes with easily available 1,4-dimethyl-2,3-diisopropylcyclopentadienide or its silylated derivative show good solubility and crystallinity. Chromocenes with trimethylsilyl or tert-butyl substituents are examples for the flexibility of CSi bonds in contrast to CC bonds. Another high spin chromocene was not found among the silylated or alkylated examples.Figure optionsDownload as PowerPoint slide